1. Technical Field of the Invention
This invention relates generally to radios and more particularly to reducing adjacent channel interference in a radio receiver.
2. Description of Related Art
As is known, handheld digital audio systems are becoming very popular. Such systems include digital audio players/recorders that record and subsequently playback MP3 files, WMA files, etc. Such digital audio players/recorders may also be used as digital dictaphones and file transfer devices. Further expansion of digital audio players/recorders includes providing a frequency modulation (FM) radio receiver such that the device offers FM radio reception.
As with most radio receivers, including FM receivers, the ability to accurately reproduce the received RF signal is dependent upon a number of factors. These factors include signal-to-noise ratio, adjacent channel interference, distortion, noise floor, et cetera. Accordingly, a well designed radio receiver addresses each of these factors. For example, to address the adjacent channel interference, many receivers will include a narrow band filter that attenuates adjacent channels while passing substantially unattenuated the desired channel. Such an implementation works well when the channels are relatively widely spaced (e.g., are spaced wider than the bandwidth of an economical narrow band filter).
In situations where the channels are relatively close together (e.g., the channel spacing is less than the bandwidth of an economical narrow band pass filter), adjacent channel interference is still a factor. Thus, the designer of a radio receiver needs to make a tradeoff between the level of adjacent channel interference and the complexity and cost of designing a narrow band pass filter. Such an issue exists with frequency modulated (FM) radio receivers. For high end FM receivers, a designer may utilize a more complex and expensive narrow band pass filter to attenuate adjacent channels. However, for more typical commercial grade FM receivers, such a complex and expensive narrow band pass filter is not feasible. As such, for many FM receivers, a certain level of adjacent channel interference is to be expected especially in regions where there are numerous FM radio stations.
Therefore, a need exists for a method and apparatus to reduce adjacent channel interference in radio receivers, including FM radio receivers.